Display screen or portion thereof for a transitional graphical user interface



FIG. 1 is a front view of a first image in a sequence for a display screen or portion thereof for a transitional graphical user interface showing my new design;

FIG. 2 is a front view of a second image thereof;

FIG. 3 is a front view of a third image thereof;

FIG. 4 is a front view of a fourth image thereof; and,

FIG. 5 is a front view of FIG. 1 which illustrates an example environment.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 through 4. This process or period forms no part of the claimed design. The long and short dashed broken line showing of a mobile terminal in FIGS. 1-4 forms no part of the claimed design. The mobile terminal, display screen, and the text, numbers, symbols and images of the graphical user interface shown in broken line in FIGS. 1 through 5 form no part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof for a transitional graphical user interface, as shown and described. 